1. Field of the Invention
The present invention pertains to wrenches. In particular, it pertains to hydraulic wrenches of the type normally referred to as hydraulic torque wrenches.
2. Brief Description of the Prior Art
There are many situations in industry where it is necessary to assert relatively large torques on nuts or similar threaded fasteners. For example, there are millions of flange type connections in use which are fastened by threaded studs and nuts. In the past, conventional hand wrenches have been used for this purpose. However, it is sometimes difficult for one or even two men to apply the necessary torque to some of these connections, even by using a "cheater" device for extending the leverage of the wrench.
Furthermore, the hand wrenches of the past are not completely safe. Particularly when a cheater device is used, a hand wrench may slip causing injury to the user. They may also be hazardous in potentially combustible areas such as are frequently found in refineries and chemical plants, due to the possibility of sparks being generated when a wrench or cheater device slips. Governmental regulations of today generally forbid such unsafe practices.
Even if enough force can be applied manually to tighten the threaded connection, there may be lack of uniformity in a connection involving several threaded fasteners, such as in a flange connection. In many of the high-pressure industrial applications of today, it is essential that all fasteners are uniformly tightened and placed under uniform tension.
Because of the drawbacks of manual wrench tightening, several powered wrench devices have been developed over the years, including impact wrenches, geared wrenches and hydraulic wrenches. One of the most satisfactory in applying the necessary torque and in controlling the amount of torque applied is the hydraulic torque wrench. Examples of such wrenches are those disclosed in U.S. Pat. Nos. 3,745,858 and 3,930,776.
A typical hydraulic torque wrench will include an elongated body on which is carried a drive assembly connected to a socket member for engaging and rotating a threaded nut. The drive assembly may include some sort of ratchet device for allowing rotation in one direction but preventing it in the opposite. The drive assembly may include a lever arm, to which one end of a hydraulic ram or power unit may be connected, the opposite end of the power unit being connected to the body. During the power stroke, the hydraulic ram will be extended, moving the lever arm of the drive assembly and rotating the socket connected thereto. On the return stroke of the hydraulic ram, the ratchet device permits lost motion, applying no torque to the nut, so that the drive assembly can be repositioned for continued application of torque during the next power stroke of the hydraulic ram.
To apply the necessary force during the power stroke of the hydraulic ram, it is necessary to restrain the fixed end of the ram. This is generally accomplished by providing a reaction surface on the wrench body for resting against a suitable fixed object. Many times, there is no fixed object directly contactable by the body of the wrench and even if there is, it may be undesirable to react against it. For example, the fixed object may be a thin wall pipe which could be damaged by the reaction force.